Ceramic honeycomb structure

ABSTRACT

A honeycomb structural body comprises one or plural pillar-shaped porous ceramic members in which many through-holes are arranged side by side in a longitudinal direction through partition walls and either one end portions of these through-holes are sealed. The partition wall forming the structural body has a surface roughness of not less than 10 μm as a maximum roughness Rz defined in JIS B0601-2001 and an average pore size of 5-100 μm in a pore distribution measured by a mercury pressure method, and satisfies the following relationship: 
 
A≧90−B/20 or A≦100−B/20 
when a ratio pores having a pore size of 0.9-1.1 times the average pore size to total pore volume is A (%) and a thickness of the partition wall is B (μm), and there is proposed an effective honeycomb structural body having excellent pressure loss and catching efficiency and a high catalyst reactivity.

TECHNICAL FIELD

This invention relates to a ceramic honeycomb structural bodyeffectively used as a filter or the like for removing particulates in anexhaust gas discharged from an internal-combustion engine such as adiesel engine or the like.

BACKGROUND ART

The exhaust gas discharged from internal-combustion engines in a vehiclesuch as bus, truck or the like, or a construction machine and the likecontains particulates exerting upon an environment or human body, sothat it is demanded to develop a technique removing the particulates.For example, as one of such techniques, there is a honeycomb structuralbody (filter) for the purification of the exhaust gas as shown in FIG. 1wherein the exhaust gas is passed through porous ceramic members tocatch and remove the particulates.

As one example of the honeycomb structural body for the purification ofthe exhaust gas, there is a ceramic honeycomb filter 20 as shown in FIG.2 wherein a plurality of square-pillar shaped porous ceramic members(units) 30 are combined through seal material layers 23 to constitute aceramic block 25 and a seal material layer 24 for preventing leakage ofan exhaust gas is formed around the ceramic block 25. The porous ceramicmember 30 has a function as a filter wherein the particulates are caughtby partition walls when the exhaust gas passes through partition walls33 separating the plurality of the through-holes 31 arranged side byside in the longitudinal direction (wall flow).

The through-holes 31 formed in the porous ceramic member (unit) 30 areclogged at either end portions of inlet side and outlet side for theexhaust gas with a sealing material 32 (preferably in the form ofcheckered patter) as shown in FIG. 2 b, in which the exhaust gas flownfrom one end portion of the through-hole 31 passes through the partitionwall 33 separating the through-hole 31 and flows out from the other endportion of adjoining through-hole 31.

Moreover, the seal material layer 24 disposed on the outer periphery forpreventing the leakage of the exhaust gas from the outer peripheralportion of the ceramic block 25 when the honeycomb filter 20 is disposedin an exhaust pipe of an internal-combustion engine as previouslymentioned.

Such a ceramic honeycomb filter 20 is now used in large-size vehicles,vehicles provided with a diesel engine and the like because it isexcellent in the heat resistance and easy in the regeneration treatment.

In the honeycomb filter 20 for the purification of the exhaust gas, ithas hitherto been mainly made to adjust the catching efficiency and thepressure loss by adjusting pore size and pore distribution of poresproduced in the porous sintered body (partition walls) or adjusting wallthickness and pore distribution thereof.

For example, Japanese Patent No. 3272746 (hereinafter referred to asarticle 1) discloses a diesel particulate filter having an average poresize of 1-15 μm and a standard deviation of pore size distributionrepresented by a common logarithm of the pore size of not more than0.20.

Also, Internal Publication WO 02/26351 (hereinafter referred to asarticle 2) discloses a catalyst-carried filter having an average poresize of 10-250 μm and a standard deviation of pore size distributionrepresented by a common logarithm of the pore size of not more than0.40.

Furthermore, JP-A-2001-269522 (hereinafter referred to as article 3)discloses a ceramic sintered body filter wherein the wall thickness ismade thick in the production of the filter using material having aplurality of larger pores and the wall thickness is made thin in theproduction of the filter using a material having a plurality of smallpores.

Moreover, JP-A-2003-1029 (hereinafter referred to as article 4)discloses a porous ceramic honeycomb filter having a porosity of cellwall of 55-75%, an average pore size of 10-40 μm and a surface roughness(maximum height Ry) of not less than 10 μm.

However, the exhaust gas filters described in the articles 1 and 2 tendto make the surface roughness small because the pore size distributionof the filter becomes extremely uniform. In this case, as the surfaceroughness becomes small, the surface roughness of the catalyst coatinglayer becomes also small, so that there is a problem that the reactionsite of the catalyst coating layer with the particulates becomes lessand the supply of oxygen is insufficient and hence the catalyticreaction becomes insufficient

In the ceramic filter disclosed in the article 3, the distributionamount of the pores and the wall thickness are defined, and it isdescribed to arrange fine pores to the thin wall and large pores to thethick wall, but pores having approximately the same size are dispersedat a uniform density, so that the surface roughness becomessubstantially small likewise the articles 1, 2.

Further, the honeycomb filter disclosed in the article 4 is insufficientin the countermeasure to the pressure loss or the like because the poredistribution is not examined.

DISCLOSURE OF THE INVENTION

The invention is made for solving the aforementioned problems of theconventional techniques and an object thereof is to provide an effectivestructure of a ceramic honeycomb structural body being excellent in thepressure loss and the catching efficiency and high in the catalyticreactivity.

The inventors have repeatedly made experiments by changing pore-formingmaterials for adjusting a pore distribution in a honeycomb structuralbody in order to achieve the above object and found that even if thepore distributions measured by a mercury pressure method are within thesame numerical range, the combustion characteristics of particulateschange in accordance with the surface roughness of the partition walland the thickness of the partition wall.

Now, the inventors have further found that in the ceramic honeycombstructural body having the specified pore distribution in the relationwith the surface roughness of the partition wall and the thickness ofthe partition wall, even when a catalyst is carried on the surface ofthe partition walls, although the surface roughness becomes somewhatsmall, there is not brought about the lowering of the catchingefficiency of the particulate and the increase of the pressure loss, andas a result, the invention has been accomplished based on thisknowledge.

That is, the ceramic honeycomb structural body of the invention is aceramic honeycomb structural body comprised of one or pluralpillar-shaped porous ceramic members in which a plurality ofthrough-holes are arranged side by side in a longitudinal directionthrough partition walls and either one end portions of thesethrough-holes are sealed, characterized in that the partition wallforming the structural body has a surface roughness of not less than 10μm as a maximum roughness Rz defined in JIS B0601-2001 and an averagepore size of 5-100 μm in a pore distribution measured by a mercurypressure method, and satisfies the following relationship:A≧90−B/20 or A≦100−B/20when a ratio pores having a pore size of 0.9-1.1 times the average poresize to total pore volume is A (%) and a thickness of the partition wallis B (μm).

Moreover, the invention is not a technique of adjusting the pressureloss and the catching efficiency by merely controlling the poredistribution measured by the mercury pressure method. Because, when thepore distribution of the surface of the partition wall is merelyadjusted, if a catalyst is coated, the irregularity of the surface ofthe partition wall is lacking and the reactivity of the catalyst isdeteriorated.

In general, even if the value of pore distribution in the partitionwalls is the same, there may be caused a large difference in theperformances of the filter between the case that only shallow pores areexistent on the surface (FIG. 4(b)) and the case that extremely deeppores and shallow pores are existent together (FIG. 4(a)). For example,when a catalyst coating is conducted on a surface of a honeycombstructural body in which there is a little difference in the depths ofthe pores on the partition wall surface, in the case (FIG. 3(b)), thepores are completely filled with a catalyst coating layer (hereinafterreferred to as catalyst coat layer) to quite clog the surface of thestructural body.

From this fact, as the ceramic member for the honeycomb filter accordingto the invention, the surface roughness Rz is defined for enhancing thereactivity of the catalyst after the catalyst coating in addition to thedefinition of the pore distribution in accordance with the partitionwall thickness.

In the invention, the roughness of the wall portion partitioning thethrough-holes in the porous ceramic member, i.e. of the surface of thepartition wall is preferable to be not more than 100 μm as a maximumroughness Rz defined in JIS B0601-2001, and also it is preferable toform a catalyst coating layer on the surface of the partition wallseparating the through-holes. It is preferable that a plurality ofporous ceramic members are bundled so as to interpose a sealing materiallayer between the members in the formation of a combination of theseporous ceramic members, and this member is preferable to be siliconcarbide ceramic. Such a combination is preferable to be used as a filterfor the exhaust gas purification apparatus in the vehicle.

The construction of the ceramic honeycomb structural body according tothe invention will be described in detail below.

A first invention lies in a ceramic honeycomb structural bodycharacterized in that the partition wall has a surface roughness of notless than 10 μm as a maximum roughness Rz defined in JIS B0601-2001 andan average pore size of pore distribution as measured by a mercurypressure method is 5-100 μm and when a ratio of pores having a pore sizeof 0.9-1.1 times the average pore size to a total pore volume is A (%)and a thickness of the partition wall is B (μm), they satisfy thefollowing relation:A≧90−B/20.

The above equation (A≧90−B/20) shows that a constant relation isestablished between the thickness of the partition wall and the poredistribution. For example, as the thickness of the partition wallbecomes thin, it is desirable to form relatively uniform pores beingless in the scattering to the average pore size, while as the thicknessof the partition wall becomes thick, it allows to form a somewhatnon-uniform pore size distribution being large in the scattering to theaverage pore size. When the partition wall is formed under the abovestandard, various characteristics such as catching efficiency ofparticulate, pressure loss and the like can be improved.

Although the mechanism is not clear, when the pore distribution is madeuniform, the disorder of the exhaust gas flow due to the difference ofpore sizes is hardly caused, and hence the catching efficiency isincreased and the pressure loss is reduced. Further, it is consideredthat there is caused no difference in the flow amount of the exhaust gasthrough the partition wall and hence the particulates can be uniformlycaught as a whole and the leakage of the particulates hardly causes tofurther improve the catching efficiency.

Also, in case that the thickness of the partition wall is thin, theparticulates (soot) are caught only in the surface of the partitionwall, while in case of the thick wall thickness, the particulates can becaught not only on the wall surface but also in the inside thereof. Inthe latter case, the layer of the particulates adhered to the wallsurface becomes thin, so that the catching efficiency increases and thepressure loss reduces as a whole.

Then, noticing the reaction efficiency with the catalyst, when the poresize distribution in the partition wall is made uniform, there is causedno disorder of the exhaust gas flow due to the difference of pore sizesand hence there is caused no difference in the flow amount of theexhaust gas and the uniform reaction can be expected as a whole. Also,the reaction efficiency is affected by the wall thickness. That is, itis possible to conduct the reaction on the wall surface in case of thethin wall thickness and to conduct the reaction up to the inside of thewall in case of the thick wall thickness. Therefore, as the wallthickness becomes thicker, a probability of contacting the particulateor the exhaust gas with the catalyst on the catalyst coat layer becomeshigh and the reactivity is improved.

In this meaning, the invention determines the wall thickness and thepore size distribution based on the above equations.

Next, in the invention, it is required that the surface roughness Rz ofthe partition wall represented by the maximum roughness is not less than10 μm. In general, the surface roughness (irregularity) resulted fromthe ceramic particles themselves is existent in the porous body, but thesurface roughness thereof is small. Since the particulates are comprisedof carbon fine particles, sulfur based fine particles such as sulfate orthe like, fine particles of high molecular weight hydrocarbon or thelike, even if the particle size is 20-700 nm, these particles arefrequently aggregated to form secondary particles of about 0.1-10 μm.Therefore, when the surface roughness of the partition wall surface issmall, the particulates fill spaces between ceramic particlesconstituting the porous body and are stored at a state ofcompact-filling in the pores, so that the irregularity of the wallsurface is substantially removed and the pressure loss becomes high.Further, even if it is intended to lower the pressure loss byregeneration, since the aggregated particulates hardly causing thereaction are compact-filled in the pores, there is a problem that theregeneration reaction hardly occurs.

In the invention, therefore, the surface roughness is made relativelylarge for improving the reactivity in the regeneration. From this fact,it is considered that various flows of the exhaust gas are formed tohardly cause the compact-filling of the particulates though themechanism is not clear. Also, it is considered that a ceramic memberfacilitating the supply of oxygen or the like and easily causing thecatalyst reaction can be prepared by forming the various flows of theexhaust gas to make the flow-in and out of the gas become violent.

Moreover, when the surface roughness of the ceramic member is madelarge, it is sufficient to make the surface roughness of the wallportion after the coating of the catalyst relatively large.

A second invention lies in a ceramic honeycomb structural bodycharacterized in that the wall portion has a surface roughness of notless than 10 μm as a maximum roughness Rz defined in JIS B0601-2001 andan average pore size of pore distribution as measured by a mercurypressure method is 5-100 μm and when a ratio of pores having a pore sizeof 0.9-1.1 times the average pore size to a total pore volume is A (%)and a thickness of the wall is B (μm), they satisfy the followingrelation:A≦100−B/20.

The equation (A≦100−B/20) shows a relation between pore distribution andwall thickness contributing to the catching efficiency and pressure losslikewise the first invention. For example, as the wall thickness becomesthinner, it is desirable to provide a relatively uniform poredistribution being less in the scattering against the average pore size,while as the wall thickness becomes thicker, it is preferable to providea somewhat non-uniform pore distribution being large in the scatteringagainst the average pore size. In this case, however, it is notpreferable that the pore distribution to the wall thickness is toouniform different from the equation of the first invention, so that thesecond invention has a feature in a point that the equation iscorrected.

That is, if the pore distribution is too uniform, it is considered thatalthough the mechanism is not clear, the particulates having the sameform generated from an engine at the same period are instantaneouslystored so as to uniformly fill in pores of particles constituting theporosity and hence the pressure loss rapidly rises and also they arestored so as to remove the irregularity of the wall surface to therebyincrease the pressure loss.

In the invention, therefore, the above equation is attained based on theknowledge that it is effective to intentionally make the partiallynon-uniformity of the pores by giving a certain scattering to the poresize. It is considered that when the certain scattering is produced inthe pore size of the pores, the catching efficiency and pressure losscan be more improved and the reactivity in the formation of the catalystcoat layer can be improved.

In the invention, it may be preferable that the surface roughness Rz isnot more than 100 μm.

In the above first and second inventions, there is provided a ceramicstructural body that as the wall thickness becomes thinner, the poresize is made uniform to the average pore size, while as the wallthickness becomes thicker, the pore distribution is made somewhatnon-uniform to the average pore size.

However, when the surface roughness Rz is larger than 100 μm, at leasttwo kinds of pore having a very deep concave portion (valley) being finein pore diameter and pore having a very high convex portion (mountain)being fine in pore diameter. As a result, it is considered that if theparticulates are thinly and uniformly stored in the deep part of theconcave portion (valley), the reactivity is improved likewise the firstinvention. However, even when the particle size of the particulate isusually 20-700 nm, these particulates are frequently aggregated to formsecondary particles of about 0.1-10 μm, so that it is difficult tothinly and uniformly catch the particulates and hence the secondaryparticles of the aggregated particulates are filled and adsorbed on theway of the concave portion (valley) so as to clog the concave portion tomake the surface roughness small. Therefore, the significance of theinvention defining the surface roughness is lost and it is consideredthat the pressure loss becomes high and the reactivity becomes bad as inthe conventional technique.

In the invention, when the catalyst coat layer is formed on the surfaceof the partition wall, since the pore distribution is controlled to asmall value, as the surface roughness Rz becomes more than 100 μm, thecatalyst coat layer is not formed up to a deeper depth of the pores inthe filter and as a result, coating is caused and finally the reactivityis poor.

Moreover, the ceramic honeycomb structural body according to theinvention is constituted to include the pillar-shaped porous ceramicmember in which many through-holes are arranged side by side in thelongitudinal direction through the partition walls. In this case,however, the porous ceramic member may be constituted by bundling aplurality of the pillar-shaped porous ceramic members in which manythrough-holes are arranged side by side in the longitudinal directionthrough the partition walls with a sealing material layer (hereinafterreferred to as an aggregate type honeycomb filter) or may be constitutedwith the ceramic members integrally united with each other as a whole(hereinafter referred to as one-piece type honeycomb filter).

In case of the aggregate type honeycomb filter, the wall portion isconstituted with the partition wall separating the through-holes of theporous ceramic member and the sealing material layer functioning as anadhesive layer for the outer wall of the porous ceramic member andbetween the porous ceramic members. In case of the one piece typehoneycomb filter, the wall portion is constituted with one kind of thepartition walls.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically showing an embodiment ofapplying the ceramic honeycomb structural body according to theinvention to the honeycomb filter.

FIG. 2(a) is a perspective view schematically showing an embodiment ofthe porous ceramic member (unit) constituting the honeycomb filter shownin FIG. 1, and FIG. 2(b) is a section view taken along a line A-A of theporous ceramic member.

FIG. 3(a) is a perspective view schematically showing another embodimentof applying the ceramic honeycomb structural body according to theinvention to the honeycomb filter, and FIG. 3(b) is a section view takenalong a line B-B of the filter shown in FIG. 3(a).

FIG. 4 is a view explaining a surface roughness of a partition wall inthe honeycomb filter according to the invention.

FIG. 5 is a graph showing a relation between pore distribution ratio andpressure loss in a filter of Example 1.

FIG. 6 is a graph showing a relation between pore distribution ratio andcatching efficiency in a filter of Example 1.

FIG. 7 is a graph showing a relation between surface roughness andcatching efficiency in a filter of Example 1.

FIG. 8 is a graph showing a relation between surface roughness andregeneration ratio in a filter of Example 1.

FIG. 9 is a graph showing a relation between a graph showing a relationbetween surface roughness and catching efficiency in a filter of Example1.

FIG. 10 is a graph showing a relation between surface roughness andregeneration ratio in a filter of Example 1.

FIG. 11 is a graph showing a relation between pore distribution ratioand pressure loss in a filter of Example 2.

FIG. 12 is a graph showing a relation between pore distribution ratioand catching efficiency in a filter of Example 2.

FIG. 13 is a graph showing a relation between surface roughness andcatching efficiency in a filter of Example 2.

FIG. 14 is a graph showing a relation between surface roughness andregeneration ratio in a filter of Example 2.

FIG. 15 is a graph showing a relation between a graph showing a relationbetween surface roughness and catching efficiency in a filter of Example2.

FIG. 16 is a graph showing a relation between surface roughness andregeneration ratio in a filter of Example 2.

FIG. 17 is a graph showing a relation between pore distribution ratioand pressure loss in a filter of Example 3.

FIG. 18 is a graph showing a relation between pore distribution ratioand catching efficiency in a filter of Example 3.

FIG. 19 is a graph showing a relation between surface roughness andcatching efficiency in a filter of Example 3.

FIG. 20 is a graph showing a relation between surface roughness andregeneration ratio in a filter of Example 3.

FIG. 21 is a graph showing a relation between a graph showing a relationbetween surface roughness and catching efficiency in a filter of Example3.

FIG. 22 is a graph showing a relation between surface roughness andregeneration ratio in a filter of Example 3.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a perspective view schematically showing a concrete example ofan aggregate type honeycomb filter as an embodiment of the honeycombstructural body according to the invention, and FIG. 2(a) is aperspective view schematically showing an embodiment of a porous ceramicmember constituting the honeycomb filter shown in FIG. 1, and FIG. 2(b)is a section view taken along a line A-A of the porous ceramic member.

As shown in FIGS. 1 and 2, in the ceramic honeycomb structural body 20(hereinafter called as a honeycomb filter) of the invention, a pluralityof porous ceramic members 30 are bundled through sealing material layers23 to form a ceramic block 25, and a sealing material layer 24 forpreventing leakage of an exhaust gas is formed around the ceramic block25.

Also, many through-holes 31 are arranged side by side in the porousceramic member 30 in its longitudinal direction, in which end portionsof the through-holes at either inlet side or outlet side for the exhaustgas are sealed with a plugging material 32 and partition walls 33separating these through-holes from each other function as a filter.

When the honeycomb filter 20 having the above construction is disposedas a filter in an exhaust path of an internal combustion engine such asa diesel engine or the like, particulates discharged from the internalcombustion engine are caught by the partition walls 23 in the passingthrough the honeycomb filter 20 to purify the exhaust gas (wall flowtype).

In the honeycomb filter 20 shown in FIG. 1, the form is cylindrical, butthe honeycomb structural body according to the invention is not limitedto the cylindrical form and may be, for example, ellipsoidal, prismaticsuch as triangular, rectangular, hexagonal or the like.

In the honeycomb structural body according to the invention, as amaterial for the porous ceramic member are used nitride ceramics such asaluminum nitride, silicon nitride, boron nitride, titanium nitride andthe like, carbide ceramics such as silicon carbide, zirconium carbide,titanium carbide, tantalum carbide, tungsten carbide and the like, andoxide ceramics such as alumina, zirconia, cordierite, mullite and thelike. Among them, silicon carbide being large in the heat resistance,excellent in the mechanical properties and large in the thermalconductivity is desirable.

As the ceramic may be further used silicon-containing ceramic compoundedwith metallic silicon, ceramics bonded with silicon or silicate compoundand the like.

Also, “silicon carbide ceramic” used in the invention is a ceramiccomposed mainly of silicon carbide, which includes ones obtained bybonding silicon carbide with a metal, or a crystalline or amorphouscompound in addition to only silicon carbide.

The porous ceramic member is desirable to have a porosity (pore ratio)of about 20-80%, more preferably 50-70%. When the porosity is less than20%, the honeycomb filter may cause the clogging immediately, while whenthe porosity exceeds 80%, the porous ceramic member is easily broken dueto the lowering of the strength. In case of applying the catalyst, therise of the pressure loss becomes violent, so that it is desirable to be50-70%.

The porosity can be measured by the conventionally known method such asmercury pressure method, Archimedes method, measurement through scanningtype electron microscope (SEM) or the like.

The porous ceramic member is desirable to have an average pore size(diameter) of 5-100 μm. When the average pore size is less than 5 μm,the particulates may easily cause the clogging, while when the averagepore size exceeds 100 μm, the particulates pass through the pores andthe catching of the particulates is impossible and the function as thefilter can not be fulfilled.

The particle size of the ceramic used in the production of the porousceramic member is not particularly limited, but it is desirable thatshrinkage is less at subsequent firing step. For example, it isdesirable to combine 100 parts by weight of powder having an averageparticle size of about 0.3-50 μm and 5-65 parts by weight of powderhaving an average particle size of about 0.1-1.0 μm. The porous ceramicmember can be produced by mixing ceramic powders having the aboveparticle sizes at the above compounding amounts.

In the invention, the honeycomb structural body has a structure thatboth end portions are plugged for catching the particulates. Also, theplugging material is preferable to be made of porous ceramic.

In the honeycomb filter according to the invention, the pluggingmaterial is preferable to use the same porous ceramic as in the porousceramic member. Because, the adhesion strength between both can beincreased, and the porosity of the plugging material is adjusted to thesame as in the porous ceramic member, whereby it can be attempted tomatch the thermal expansion coefficient of the porous ceramic memberwith the thermal expansion coefficient of the plugging material and itcan be prevented to cause a gap between the plugging material and thepartition wall through thermal stress in the production or use or tocause cracks in the plugging material or a portion of the partition wallcontacting with the plugging material.

When the plugging material is made of the porous ceramic, as thematerial can be used the same material as the ceramic materialconstituting the porous ceramic member.

The plugging material can be formed by filling a slurry of the ceramicpowders, or may be formed by joining the previously produced pluggingpieces.

In the filter of the invention, the sealing material layer 23 is formedbetween the porous ceramic members 20 and the sealing material layer 24is formed on an outer periphery of the ceramic block 25. The sealingmaterial layer 23 formed between the porous ceramic members 30 functionsas an adhesive bundling the plural porous ceramic members 30 with eachother, while the sealing material layer 24 formed on the outer peripheryof the ceramic block 15 functions as a sealing material for preventingthe leakage of the exhaust gas from the outer periphery of the ceramicblock 25 when the filter 20 according to the invention is disposed inthe exhaust path of the internal combustion engine.

As the material constituting the sealing material layer is used, forexample, an inorganic binder, an organic binder, inorganic fibers and/orinorganic particles or the like.

As mentioned above, in the filter of the invention, the sealing materiallayer is formed between the porous ceramic members or on the outerperiphery of the ceramic block, but these sealing material layers may bemade of the same material or may be made of different materials.Further, when the sealing material layers are made of the same material,the compounding ratio of these materials may be the same or different.

As the inorganic binder is used, for example, silica sol, alumina sol orthe like. They may be used alone or in a combination of two or more.Among the above inorganic binders, silica sol is desirable.

As the organic binder are used, for example, polyvinyl alcohol, methylcellulose, ethyl cellulose, carboxymethyl cellulose and the like. Theymay be used alone or in a combination of two or more. Among the aboveorganic binders, carboxymethyl cellulose is desirable.

As the inorganic fiber is used a ceramic fibers of silica-alumina,mullite, alumina, silica or the like. They may be used alone or in acombination of two or more. Among the inorganic fibers, silica-aluminafiber is desirable.

As the inorganic particle are used, for example, carbides, nitrides andthe like. Concretely, there are used inorganic powder or whisker made ofsilicon carbide, silicon nitride, boron nitride or the like. They may beused alone or in a combination of two or more. Among these inorganicparticles, silicon carbide having an excellent thermal conduction isdesirable.

The sealing material layer 23 may be made of a densified body or aporous body capable of flowing the exhaust gas into an inside thereof.The sealing material layer 24 is desirable to be made of the densifiedbody. Because, the sealing material layer 24 is formed for the purposeof preventing the leakage of the exhaust gas from the outer periphery ofthe ceramic block 25 when the filter 20 is arranged in the exhaust pathof the internal combustion engine.

FIG. 3(a) is a perspective view schematically showing a concrete exampleof a one piece type filter as an embodiment of the honeycomb filteraccording to the invention, and FIG. 3(b) is a section view taken alonga line B-B.

As shown in FIG. 3(a), the honeycomb filter 10 is constituted byincluding a pillar-shaped porous ceramic block 15 in which manythrough-holes 11 are arranged side by side in the longitudinal directionthrough wall portions 13.

Also, many through-holes 11 are arranged side by side in thelongitudinal direction of the pillar-shaped porous ceramic block 15 inwhich the end portions at either inlet side or outlet side for theexhaust gas are plugged with a plugging material 12 and partition walls13 separating the through-holes 11 from each other serve as a filter.

In the honeycomb filter 10, the porous ceramic block 15 has the sameconstruction as in the filter 20 except a one piece structure producedby sintering, so that the exhaust gas flowed therein passes through thewall portions 13 separating the through-holes from each other and isdischarged therefrom.

In the honeycomb filter 10 according to the invention, the pillar-shapedporous ceramic block 15 is desirable to have a porosity (pore ratio) of20-80%, more preferably 50-70%. When the porosity of the porous ceramicblock 15 is less than 20%, the filter 10 may cause the cloggingimmediately, while when the porosity of the porous ceramic block 15exceeds 80%, the filter 10 is easily broken due to the lowering of thestrength. Particularly, the rise of the pressure loss becomes violent inthe application of the catalyst, so that it is desirable to be 50-70%.

The size of the porous ceramic block 15 is not particularly limited, butis determined by considering the size of the exhaust path in theinternal combustion engine used and the like. Also, the shape is notparticularly limited as far as it is pillar-shaped, and may be, forexample, cylindrical, ellipsoidal, prismatic or the like, but there isusually used a cylinder as shown in FIG. 3.

As the porous ceramic constituting the porous ceramic block 15 are used,for example, an oxide ceramic such as cordierite, alumina, silica,mullite or the like; a carbide ceramic such as silicon carbide,zirconium carbide, titanium carbide, tantalum carbide, tungsten carbideor the like; a nitride ceramic such as aluminum nitride, siliconnitride, boron nitride, titanium nitride or the like; and so on, but theoxide ceramic such as cordierite or the like is usually used. Because,it can be produced cheaply and is relatively low in the thermalexpansion coefficient and is not oxidized in use.

The porous ceramic block 15 is desirable to have an average pore size ofabout 5-100 μm. When the average pore size is less than 5 μm, theparticulates may easily cause the clogging, while when the average poresize exceeds 100 μm, the particulates pass through the pores and thecatching of the particulates can not be conducted and the function asthe filter can not be fulfilled.

The sealing material in the honeycomb filter 10 is desirable to be madeof porous ceramic. When the sealing material is made the same as in theporous ceramic block 15, the adhesion strength between both can beenhanced, while by adjusting the porosity of the sealing material so asto satisfy the above condition, it can be attained to match the thermalexpansion coefficient of the porous ceramic block 15 with the thermalexpansion coefficient of the sealing material, whereby it can beprevented to cause a gap between the plugging material and the wallportion 13 through thermal stress in the production or use or to causecracks in the plugging material or a portion of the wall portion 13contacting with the plugging material.

When the sealing material is made of the porous ceramic, the materialtherefor is not particularly limited and may mention the same materialas the ceramic material constituting the porous ceramic block 15.Moreover, the sealing material may be formed by filling a slurry ofceramic powder or by joining sealing pieces previously produced.

In the honeycomb filter of the invention having the construction asshown in FIGS. 1 and 3, the form of the section of the through-holeperpendicular to the longitudinal direction (hereinafter referred to assection simply) is desirable to be polygonal.

In the invention, the section of the through-hole may be a polygon suchas square, pentagon, octagon or the like, or a trapezoid, or may be amixture of various polygons.

A. An embodiment of the production method of the honeycomb filteraccording to the invention will be described below.

a. When the honeycomb filter according to the invention is a one piecefilter constituted with a sintered body as a whole as shown in FIG. 3, astarting paste composed mainly of the aforementioned ceramic is firstextrusion-molded to prepare a ceramic shaped body having substantiallythe same form as in the filter 10 of FIG. 3.

In the above extrusion molding, the starting paste is continuouslyextruded through a metal die disposed on a top portion of an extrusionmolding machine and provided with many fine holes and then cut into agiven length to prepare the ceramic shaped body. In the production ofthe honeycomb shaped body, the surface roughness of the shaped body isadjusted to not more than 100 μm by subjecting a wall face of the finehole formed in the die, a slit or the like to a polishing treatment orthe like. Because, the wall faces of the fine hole in the die and theslit are portions directly contacting with the starting paste in theextrusion molding, so that if the surface roughness of the wall face islarge, the surface roughness of the partition wall surface existing inthe through-hole of the ceramic shaped body to be prepared becomes largeand it is difficult to adjust the surface roughness of the partitionwall surface existing in the through-hole of the honeycomb filterproduced through subsequent step.

In the invention, the shape of the irregularity of the partition wallsurface is desirable to be adjusted by adjusting an aspect ratio of ahole-forming material having a hole forming action.

Moreover, the shape of the irregularity of the partition wall surfacemay be adjusted by adjusting the viscosity of the starting paste,particle size of each material, compounding ratio and the like. Thestarting paste is not particularly limited as far as it allows to renderthe porosity of the porous ceramic block after the production into20-80%, and can be used, for example, by adding a binder and adispersing medium to the powder of the aforementioned ceramic.

As the binder can be used, for example, methylcellulose, carboxymethylcellulose, hydroxyethyl cellulose, polyethylene glycol, phenolic resin,epoxy resin and the like. The compounding amount of the binder isusually desirable to be about 1-10 parts by weight based on 100 parts byweight of the ceramic powder.

As the dispersing medium can be used, for example, an organic solventsuch as benzene or the like; an alcohol such as methanol or the like;and water and so on. This dispersing medium is compounded in a properamount so as to render the viscosity of the starting paste into aconstant range.

The ceramic powder, binder and dispersing medium are mixed in anattritor or the like, sufficiently kneaded by means of a kneader or thelike and then extrusion-molded to prepare the ceramic shaped body.

Also, a shaping assistant may be added to the starting paste, ifnecessary.

As the shaping assistant are used, for example, ethylene glycol,dextrin, aliphatic acid soap, polyalcohol and the like. To the startingpaste may be added balloons of hollow microspheres composed mainly ofoxide ceramic, spherical acryl particles, hole-forming agent such asgraphite or the like, if necessary.

As the balloon are used, for example, alumina balloon, glassmicroballoon, silas balloon, fly ash balloon (FA balloon), mulliteballoon and the like. Among them, fly ash balloon is desirable.

b. Then, the ceramic shaped body is dried by using a microwave dryingmachine, hot-air drying machine, dielectric drying machine,reduced-pressure drying machine, vacuum drying machine, freeze dryingmachine and the like to form a dried body, and thereafter the dried bodyis subjected to a plugging treatment in which given through-holes of thedried body are filled with a sealing material paste as a sealingmaterial and clogged therewith. The sealing material paste is notparticularly limited as far as a porosity of a sealing material producedafter a post-process is within 20˜80%, and may mention, for example, thesame material as in the aforementioned starting paste. However, it isdesirable to prepare the sealing material by adding a lubricant,solvent, dispersant, or binder to the ceramic powder used in theaforementioned starting paste, because the settling of the ceramicparticles in the sealing material in the plugging treatment.

c. Next, the dried ceramic shaped body filled with the sealing materialis degreased and fired at a given condition to form a filter comprisedof porous ceramics and constituted with a sintered body as a whole.

In the invention, adjusted are the conditions for decreasing and firingthe dried ceramic shaped body so as to make the surface roughness large.It is therefore necessary to pass sufficient atmosphere gas through thethrough-holes when the hole-forming agent or the shape assistantvolatilizes from the ceramic member to form file holes at the decreasingand firing process.

B. An embodiment of the production method of the honeycomb filteraccording to the invention will be described below, when the honeycombfilter is an aggregate type honeycomb filter constituted by bundling aplurality of porous ceramic members through sealing material layers asshown in FIG. 1.

a. A staring paste consisting mainly of the aforementioned ceramic isextrusion-molded to form a green shaped body having a shape like aporous ceramic member 30 shown in FIG. 2. As the starting paste can beused the same starting paste as described in the aforementionedaggregate type honeycomb filter.

b. Then, the ceramic shaped body is dried by using a microwave dryingmachine or the like to form a dried body, and thereafter the dried bodyis subjected to a plugging treatment in which given through-holes of thedried body are filled with a plugging material paste as a pluggingmaterial and clogged therewith. As the plugging material paste can beused the same as in the plugging material paste described on the aboveone piece type filter. The plugging treatment can be carried out in thesame manner as in the one piece type filter except the object to befilled with the sealing material paste.

c. Next, the dried body subjected to the plugging treatment is degreasedand fired under given conditions, whereby there can be produced a porousceramic member in which a plurality of through-holes are arranged sideby side in the longitudinal direction through partition walls. In thiscase, the same method as in the one piece type filter can be used.

d. Then, a sealing material paste forming a sealing material layer 23 isapplied at a uniform thickness and a step of laminating other porousceramic member 30 is successively repeated to prepare a laminate ofsquare-pillar shaped porous ceramic members 30 having a given size. Asthe material constituting the sealing material paste is alreadymentioned in the above one piece type filter, and an explanation thereofis omitted here.

e. Next, the laminate of the porous ceramic members 30 is heated to dryand solidify the sealing material paste layer to form a sealing materiallayer 24, and thereafter an outer peripheral portion is cut into a shapeas shown in FIG. 1 with a diamond cutter or the like to prepare aceramic block 25.

A sealing material layer 23 is formed on an outer periphery of theceramic block 25 with the above sealing material paste, whereby therecan be produced a filter constituted by bundling the plurality of theporous ceramic members through the sealing material layers.

In general, when the thus produced honeycomb filter 10 is disposed inthe exhaust system of a diesel engine and used for a constant time, agreater amount of particulates are deposited on the wall portion of thehoneycomb filter 10 (partition walls) and the pressure loss becomeslarge, so that the filter is subjected to a regeneration treatment.

In the regeneration treatment, a gas heated by a heating means is flowedinto the inside of the through-holes 11 in the honeycomb filter 10 toheat the honeycomb filter 10, whereby the particulates deposited on thewall portion (partition walls) is burnt out and removed. Also, theparticulates may be burnt out and removed by using a post injectionsystem.

In the honeycomb structural body according to the invention, a catalystmay be carried on the partition wall surface for promoting thecombustion of the particulates or purifying CO, HC, NOx and the like inthe exhaust gas. When the catalyst is carried on the partition wallsurface of the honeycomb structural body, the honeycomb filter of theinvention functions as a filter for catching the particulates in theexhaust gas but also functions as a catalyst carrier for purifying CO,HC, NOx and the like included in the exhaust gas.

The catalyst is not particularly limited as far as it can purify the CO,HC, NOx and the like in the exhaust gas, and includes, for example, anoble metal such as platinum, palladium, rhodium or the like. Also, analkali metal (Group 1 in the periodic table), an alkaline earth metal(Group 2 in the periodic table), a rear earth element (Group 3 in theperiodic table), a transition metal element or the like may be added inaddition to the noble metal.

In the invention, a portion carrying the catalyst on the partition wallsurface of the honeycomb structural body, i.e., a catalyst coat layer isa layer formed on the surface of each ceramic particle constituting thepartition wall of the ceramic member, and the catalyst of the noblemetal used may be carried through a support layer of alumina, zirconia,titania or silica having a high specific surface area.

Next, the catalyst coat layer is explained with platinum as a catalystand alumina as a support layer.

At first, alumina powder as a support material is finely pulverized by apulverizer or the like and mixed with a solvent with stirring to preparea solution. Concretely, powder of an oxide such as y-alumina or the likeis prepared by a sol-gel method or the like. In this case, in order touse as a coat layer for a catalyst, the specific surface area is high asfar as possible, and it is desirable to have a specific surface area ofnot less than 250 m²/g. Since the specific surface area is high, it isdesirable to select γ-alumina. Such powder is added with an inorganicbinder such as hydrated alumina, alumina sol or silica sol, or withabout 5-20 wt % of a solvent such as pure water, water, alcohol, diol,polyvalent alcohol, ethylene glycol, ethylene oxide, triethanolamine,xylene or the like and pulverized to not more than about 500 nm withstirring.

As the powder is more finely pulverized, alumina layer can be uniformlyformed on the partition wall particles of the ceramic member differentfrom the conventional catalyst coat layer coated on the surface layer ofthe partition wall through wash coating.

Then, the solution containing the (metal) oxide powder is impregnated,which is dried by heating at 110-200° C. for about 2 hours and thenfired. A preferable firing temperature is 500-1000° C., which is carriedout for 1-20 hours. When the temperature is lower than 500° C., thecrystallization is not proceeded, while when it exceeds 1000° C., thecrystallization is excessively proceeded and it tends to lower thesurface area. By measuring the weight before and after this step can becalculated the carrying amount.

Moreover, it is desirable to conduct a treatment for improving thewettability to each particle surface in the partition wall of theceramic member prior to the impregnation of alumina. For example, whenthe surface of silicon carbide particle is modified with hydrogenfluoride (hydrogen acid) solution, the wettability to the catalystsolution is changed and hence the surface roughness of the partitionwall after the formation of the catalyst coat layer becomes large.

Then, the carrying of platinum is conducted. The platinum containingsolution is taken in a pipette at only an amount corresponding to thewater absorbing amount of the ceramic member and added dropwise and thendried at 110° C. for 2 hours and dried at 500-1000° C. in a nitrogenatmosphere to conduct the metallization.

The application of the catalyst-carried honeycomb filter of theinvention is not particularly limited, but it is preferable for use inan exhaust gas purification apparatus of a vehicle.

The following three examples are given in illustration of the inventionand are not intended as limitations thereof.

EXAMPLE 1

In Example 1, sample groups A1-A7, . . . E1-E7 of ceramic memberscomprising of silicon carbide are prepared by changing pore size, poresize distribution and surface roughness, and a platinum-containingalumina coat layer is formed on the surface of the ceramic member toconfirm the function and effect thereof. The production conditions ofeach sample are shown in Table 1.

The ceramic member in Example 1 is produced through the following steps(1)-(5).

-   (1) As a starting material, starting powder (silicon carbide) having    a relatively large average particle size (hereinafter referred to as    powder A) is first mixed with starting powder (silicon carbide)    having a relatively small average particle size (hereinafter    referred to as powder B).-   (2) In order to prepare a ceramic member having a target pore size    distribution, acryl resin particles having various shapes (density:    1.1 g/cm³) (which is called as powder C) is mixed with the starting    powder of powder A and powder B (silicon carbide starting powder) at    a given mixing ratio (vol %).-   (3) Then, methyl cellulose as a shaping assistant is mixed at a    given ratio (wt %) to the silicon carbide starting powder and    thereafter a dispersing medium consisting of an organic solvent and    water is added and all of the starting materials are kneaded.-   (4) The mixture is extrusion-molded with a mold changing a surface    roughness of a mold slit so as to form a target honeycomb form,    whereby a honeycomb shaped body having many through-holes is formed    and either one end portions of these through-holes are plugged in a    checkered pattern to obtain a honeycomb shaped body.-   (5) Finally, the shaped body is dried at 150° C. and degreased at    500° C. and fired in an inert gas atmosphere while passing through    the through-holes at a flow amount shown in Table 1 to obtain sample    groups A1-A7, B1-B7 . . . E1-E7 of honeycomb ceramic member made of    silicon carbide sintered bodies having a thickness of partition wall    of 300 m, a size of 34.3 mm×34.3 mm×150 mm, a cell density of 300    cells/in² and different surface roughnesses.

With respect to each sample produced through the above steps (1)-(5),the average pore size is measured by a mercury pressure method(according to JIS R1655:2003).

Concretely, each sample of the ceramic members is cut into a cubic bodyof about 0.8 mm, washed with a deionized water under an ultrasonic waveand sufficiently dried.

The measurement on each sample is carried out by using a micromeriticsautoporosimeter Autopore III9405 made by Shimazu Seisakusho. Themeasuring range is 0.2-500 μm, in which the measurement in a range of100 μm-500 μm is conducted every a pressure of 0.1 psia and themeasurement in a range of 0.2 μm-100 μm is conducted every a pressure of0.25 psia.

Moreover, the average pore size (diameter) is calculated as 4×S(integral pore area)/V (integral pore volume). The all pore sizedistribution and ratio of pore size corresponding to 0.9-1.1 times ofthe average pore size according to the invention can be calculated bycalculating a pore size of 0.9-1.1 times from the average pore size andcalculating a ratio of pore size range from pore size distributioncalculated from the measured data.

Then, each sample is cut so as to be parallel to the through-hole and asurface roughness of a partition wall in a central portion of the filter(represented by a maximum roughness Rz) is measured by means of asurface roughness measuring machine (Surfcom 920A made by Tokyo SeimitsuCo., Ltd.) to obtain results shown in Table 1.

With respect to each sample C1-C7 (maximum roughness Rz=50 μm) belongingto the sample group C having a wall thickness of 300 μm as a typicalexample among the sample groups A, B, . . . E in Example 1, samplesC1′-C7′ and C1″-C7″ are further prepared by changing the wall thicknessto 400 μm and 200 μm, respectively, and initial pressure loss of eachsample having different wall thicknesses is measured by using as afilter while flowing a gas at a section flow rate of 5 m/s. The resultsare shown in FIG. 5.

From the results of FIG. 5, as the pore distribution becomes too dense,the initial pressure loss becomes high, and also even when the poredistribution is rough, the initial pressure loss becomes high. When thewall thickness is 200 μm, the pressure loss is minimum at the poredistribution of 80-90%, and similarly the pressure loss becomes low atthe pore distribution of 75-85% when the wall thickness is 300 μm, andat the pore distribution of 70-80% when the wall thickness is 400 μm.

Then, 16 samples of each of the above C1-C7, C1′-C7′ and C1″-C7″ areprovided and bundled through a sealing material paste and cut by meansof a diamond cutter to form a cylindrical ceramic block, and further asealing material paste layer is formed on an outer peripheral portion ofthe ceramic block with the other sealing material paste, whereby ahoneycomb filter for the purification of an exhaust gas is produced.

Concrete production steps are as follows.

At first, the honeycomb ceramic members (samples) are bundled with aheat-resistant sealing material paste containing 30% by weight ofalumina fibers having a fiber length of 0.2 mm, 21% by weight of siliconcarbide particles having an average particle size of 0.6 μm, 16% byweight of silica sol, 5.6% by weight of carboxymethyl cellulose and28.4% by weight of water, which is cut by using a diamond cutter toprepare a clyndrical ceramic block having a diameter of 144 mm, aporosity of 55% and an average pore size of 10 μm.

In this case, the thickness of the sealing material layer bundling theceramic members is adjusted to 1.0 mm.

Then, a sealing material paste is prepared by mixing and kneading 23.3%by weight of ceramic fibers made of alumina silicate (shot content: 3%,fiber length: 0.1-100 mm) as an inorganic fiber, 30.2% by weight ofsilicon carbide powder having an average particle size of 0.3 μm asinorganic particles, 7% by weight of silica sol (SiO2 content in sol:30% by weight) as an inorganic binder, 0.5% by weight of carboxymethylcellulose as an organic binder and 39% by weight of water.

Next, the thus prepared sealing material paste is used to form a sealingmaterial paste layer having a thickness of 1.0 mm on the outerperipheral portion of the ceramic block. The sealing material pastelayer is dried at 120° C. to produce a cyclindrical honeycomb filter forthe purification of an exhaust gas.

Each of the honeycomb filters produced at the above steps is placed in apath from a diesel engine having a displacement of 3000 cc and anexhaust gas discharged from the engine at a driving state of arevolution umber of 3000 rpm and a torque of 40 Nm is flowed into thefilter for 3 minutes to measure a catching amount of particulates beforeand after the flowing (difference of catching amount in the presence orabsence of the filter), whereby a catching efficiency is measured. Theresults are shown in FIG. 6. As seen from this figure, when the wallthickness is thick, even if the pore distribution is rough, a certainextent of the catching amount is ensured.

Next, samples having pore distribution ratios of 85%, 80% and 75%(A3-A5, B3-B5, C3-C5, D3-D5, E3-E5) are extracted from 7 kinds ofsamples belonging to the sample groups A-E. Among the extracted samples,with respect to the samples having the pore distribution ratio of 85%(A3, B3, C3, D3, E3), there are prepared samples having a wall thicknessof 400 μm (A3′, B3′, C3′, D3′, E3′), and with respect to the sampleshaving the pore distribution ratio of 75% (A5, B5, C5, D5, E5), thereare prepared samples having a wall thickness of 200 μm (A5″, B5″, C5″,D5″, E5″).

With respect to each of these sample groups (A3′, A4, A5″), (B3′, B4,B5″), (C3′, C4, C5″), (D3′, D4, D5″), (E3′, E4, E5″), the pressure lossin the catching of particulates (soot) is measured. The data after thecatching of 6 g/L are shown in FIG. 7.

Similarly, a regeneration experiment is carried out by heating at adischarge temperature of 800° C. to obtain results shown in FIG. 8. Asshown in these figures, as the surface roughness Rz is too small or toolarge, the pressure loss is high and the regeneration ratio lowers. Aseach of these samples is cut and observed, when the surface roughness issmall, the aggregation of the particulates is observed, while even ifthe surface roughness is too large, the particulates are retained. Thisis considered due to the degree of disorder flow of the exhaust gas.

Then, each sample of the above sample groups (A3′, A4, A5″), (B3′, B4,B5″), (C3′, C4, C5″), (D3′, D4, D5″), (E3′, E4, E5″) is impregnated in a0.1% solution of hydrogen fluoride (hydrogen acid) for 1 minute andthereafter an alumina coat layer of 60 g/L is formed and 2 g/L of aplatinum (Pt) catalyst is carried on the alumina coat layer, wherebysamples having different surface roughnesses of alumina coat layer afterthe carrying of the catalyst are formed. With respect to the lattersamples, the surface roughness and initial pressure loss after thealumina coating are measured. The measured results are shown in FIG. 9.As seen from this figure, even when the surface roughness is high orlow, the pressure loss tends to be high.

Further, the regeneration experiment after the catching of 6 g/L iscarried out with respect to each sample after the formation of thecatalyst coat layer. The results are shown in FIG. 10. As seen from thisfigure, when the surface roughness is large or small, the regenerationratio is low and the incomplete burning is caused. Moreover, the surfaceroughness Rz is not more than 10 μm in case of conducting no surfacemodification.

As mentioned above, according to Example 1, in the ceramic structuralbody in which the alumina coat layer carrying 60 g/L of the catalyst isformed on the ceramic member, when soot is caught, if the surfaceroughness Rz is not less than 10 μm, the regeneration efficiency in thesoot catching of 10 g/L is high.

Also, when the surface roughness Rz is not less than 100 μm, theregeneration efficiency in the soot catching of 10 g/L becomes low.TABLE 1 Powder A Powder B Powder C Firing silicon carbide siliconcarbide acryl Shaping Dispersing tem- particle particle particle aspectvol assistant medium perature size wt % size wt % size ratio % wt % wt %° C. Sample A1 10 μm 70 0.3 μm 30 10 μm 1 3 10 18 2200 Sample A2 10 μm70 0.3 μm 30 10 μm 1.5 3 10 18 2200 Sample A3 10 μm 70 0.3 μm 30 10 μm 23 10 18 2200 Sample A4 10 μm 70 0.3 μm 30 10 μm 2.5 3 10 18 2200 SampleA5 10 μm 70 0.3 μm 30 10 μm 3 3 10 18 2200 Sample A6 10 μm 70 0.3 μm 3010 μm 3.5 3 10 18 2200 Sample A7 10 μm 70 0.3 μm 30 10 μm 4 3 10 18 2200Sample B1 10 μm 70 0.3 μm 30 10 μm 1 3 10 18 2200 Sample B2 10 μm 70 0.3μm 30 10 μm 1.5 3 10 18 2200 Sample B3 10 μm 70 0.3 μm 30 10 μm 2 3 1018 2200 Sample B4 10 μm 70 0.3 μm 30 10 μm 2.5 3 10 18 2200 Sample B5 10μm 70 0.3 μm 30 10 μm 3 3 10 18 2200 Sample B6 10 μm 70 0.3 μm 30 10 μm3.5 3 10 18 2200 Sample B7 10 μm 70 0.3 μm 30 10 μm 4 3 10 18 2200Sample C1 10 μm 70 0.3 μm 30 10 μm 1 3 10 18 2200 Sample C2 10 μm 70 0.3μm 30 10 μm 1.5 3 10 18 2200 Sample C3 10 μm 70 0.3 μm 30 10 μm 2 3 1018 2200 Sample C4 10 μm 70 0.3 μm 30 10 μm 2.5 3 10 18 2200 Sample C5 10μm 70 0.3 μm 30 10 μm 3 3 10 18 2200 Sample C6 10 μm 70 0.3 μm 30 10 μm3.5 3 10 18 2200 Sample C7 10 μm 70 0.3 μm 30 10 μm 4 3 10 18 2200Sample D1 10 μm 70 0.3 μm 30 10 μm 1 3 10 18 2200 Sample D2 10 μm 70 0.3μm 30 10 μm 1.5 3 10 18 2200 Sample D3 10 μm 70 0.3 μm 30 10 μm 2 3 1018 2200 Sample D4 10 μm 70 0.3 μm 30 10 μm 2.5 3 10 18 2200 Sample D5 10μm 70 0.3 μm 30 10 μm 3 3 10 18 2200 Sample D6 10 μm 70 0.3 μm 30 10 μm3.5 3 10 18 2200 Sample D7 10 μm 70 0.3 μm 30 10 μm 4 3 10 18 2200Sample E1 10 μm 70 0.3 μm 30 10 μm 1 3 10 18 2200 Sample E2 10 μm 70 0.3μm 30 10 μm 1.5 3 10 18 2200 Sample E3 10 μm 70 0.3 μm 30 10 μm 2 3 1018 2200 Sample E4 10 μm 70 0.3 μm 30 10 μm 2.5 3 10 18 2200 Sample E5 10μm 70 0.3 μm 30 10 μm 3 3 10 18 2200 Sample E6 10 μm 70 0.3 μm 30 10 μm3.5 3 10 18 2200 Sample E7 10 μm 70 0.3 μm 30 10 μm 4 3 10 18 2200 MoldAverage Pore Surface Firing roughness Flowing pore distribution rough-time (Ra) amount size ratio ness (Rz) Hr μm m/s μm % μm Sample A1 6 5 510 95 8 Sample A2 6 5 5 10 90 8 Sample A3 6 5 5 10 85 8 Sample A4 6 5 510 80 8 Sample A5 6 5 5 10 75 8 Sample A6 6 5 5 10 70 8 Sample A7 6 5 510 65 8 Sample B1 6 10 7 10 95 10 Sample B2 6 10 7 10 90 10 Sample B3 610 7 10 85 10 Sample B4 6 10 7 10 80 10 Sample B5 6 10 7 10 75 10 SampleB6 6 10 7 10 70 10 Sample B7 6 10 7 10 65 10 Sample C1 6 50 9 10 95 50Sample C2 6 50 9 10 90 50 Sample C3 6 50 9 10 85 50 Sample C4 6 50 9 1080 50 Sample C5 6 50 9 10 75 50 Sample C6 6 50 9 10 70 50 Sample C7 6 509 10 65 50 Sample D1 6 100 10 10 95 100 Sample D2 6 100 10 10 90 100Sample D3 6 100 10 10 85 100 Sample D4 6 100 10 10 80 100 Sample D5 6100 10 10 75 100 Sample D6 6 100 10 10 70 100 Sample D7 6 100 10 10 65100 Sample E1 6 100 15 10 95 110 Sample E2 6 100 15 10 90 110 Sample E36 100 15 10 85 110 Sample E4 6 100 15 10 80 110 Sample E5 6 100 15 10 75110 Sample E6 6 100 15 10 70 110 Sample E7 6 100 15 10 65 110

EXAMPLE 2

In Example 2, sample groups F1-F7, . . . J1-J7 of ceramic memberscomprising of silicon-silicon carbide composite are prepared by changingpore size, pore size distribution and surface roughness, and aplatinum-containing alumina coat layer is formed on the surface of theceramic member to confirm the function and effect thereof. Theproduction conditions of each sample are shown in Table 2.

The ceramic member in Example 2 is produced through the following steps(1)-(5).

-   (1) As a starting material, starting powder (silicon carbide having    a relatively large average particle size (hereinafter referred to as    powder A) is first mixed with starting powder (metallic silicon)    having a relatively small average particle size (hereinafter    referred to as powder B).-   (2) In order to prepare a ceramic member having a target pore size    distribution, acryl resin particles having various shapes (density:    1.1 g/cm³) (which is called as powder C) is mixed with the starting    powder of powder A and powder B at a given mixing ratio (vol %).-   (3) Then, methyl cellulose as a shaping assistant is mixed at a    given ratio (wt %) to the starting powder and thereafter a    dispersing medium consisting of an organic solvent and water is    added and all of the starting materials are kneaded.-   (4) Thereafter, the mixture is extrusion-molded with a mold changing    a surface roughness of a mold slit so as to form a target honeycomb    form, whereby a honeycomb shaped body having many through-holes is    formed and either one end portions of these through-holes are    plugged in a checkered pattern to obtain a honeycomb shaped body.-   (5) Finally, the shaped body is dried at 150° C. and degreased at    500° C. and fired in an inert gas atmosphere while passing through    the through-holes at a flow amount shown in Table 2 to obtain sample    groups F1-F7, G1-G7 . . . J1-J7 of honeycomb ceramic member made of    silicon-silicon carbide composite having a thickness of partition    wall of 300 μm, a size of 34.3 mm×34.3 mm×150 mm, a cell density of    300 cells/in² and different surface roughnesses.

With respect to each of these samples, the pore size distribution andsurface roughness are measured to obtain results shown in Table 2.

With respect to each sample H1-H7 (maximum roughness Rz=50 μm) belongingto the sample group H having a wall thickness of 300 μm as a typicalexample among the sample groups F, G, . . . J in Example 2, samplesH1′-H7′ and H1″-H7″ are further prepared by changing the wall thicknessto 400 μm and 200 μm, respectively, and initial pressure loss of eachsample having different wall thicknesses is measured by using as afilter while flowing a gas at a section flow rate of 5 m/s. The resultsare shown in FIG. 11. As shown in this figure, as the pore distributionbecomes too dense, the initial pressure loss becomes high, and also evenwhen it is rough, the initial pressure loss becomes high. When the wallthickness is 200 μm, the pressure loss is small at the pore distributionof 80-90%, and similarly the pressure loss becomes low at the poredistribution of 75-85% when the wall thickness is 300 μm, and at thepore distribution of 70-80% when the wall thickness is 400 μm.

Each sample of H1-H7, H1′-H7′, and H1″-H7″ is rendered into acylindrical filter (diameter: 144 mm, porosity: 55%) by using the samesealing material as in Example 1 and placed in a path from a dieselengine having a displacement of 3000 cc and an exhaust gas dischargedfrom the engine at a driving state of a revolution umber of 3000 rpm anda torque of 40 Nm is flowed into the filter for 3 minutes to measure acatching amount of particulates before and after the flowing (differenceof catching amount in the presence or absence of the filter), whereby acatching efficiency is measured. The results are shown in FIG. 12. Asseen from this figure, when the wall thickness is thick, even if thepore distribution is rough, a certain extent of the catching amount isensured.

Next, samples having pore distribution ratios of 85%, 80% and 75%(F3-F5, G3-G5, H3-H5, I3-I5, J3-J5) are extracted from 7 kinds ofsamples belonging to the sample groups F-J. Among the extracted samples,with respect to the samples having the pore distribution ratio of 85%(F3, G3, H3, I3, J3), there are prepared samples having a wall thicknessof 400 μm (F3′, G3′, H3′, I3′, J3′), and with respect to the sampleshaving the pore distribution ratio of 75% (F5, G5, H5, I5, J5), thereare prepared samples having a wall thickness of 200 μm (F5″, G5″, H5″,I5″, J5″).

With respect to each of these sample groups (F3′, F4, F5″), (G3′, G4,G5″), (H3′, H4, H5″), (I3′, I4, I5″), (J3′, J4, J5″), the pressure lossin the catching of particulates (soot) is measured. The data after thecatching of 6 g/L are shown in FIG. 13. Also, a regeneration experimentis carried out by heating at a discharge temperature of 800° C. toobtain results shown in FIG. 14. As shown in these figures, as thesurface roughness Rz is too small or too large, the pressure loss ishigh and the regeneration ratio lowers. As each of these samples is cutand observed, when the surface roughness is small, the aggregation ofthe particulates is observed, while even if the surface roughness is toolarge, the particulates are retained. This is considered due to thedegree of disorder flow of the exhaust gas.

Then, each sample of the above sample groups (F3′, F4, F5″), (G3′, G4,G5″), (H3′, H4, H5″), (I3′, I4, I5″), (J3′, J4, J5″) is impregnated in a0.1% solution of hydrogen fluoride (hydrogen acid) for 1 minute andthereafter an alumina coat layer of 60 g/L is formed and 2 g/L of aplatinum (Pt) catalyst is carried on the alumina coat layer, wherebysamples having different surface roughnesses of alumina coat layer afterthe carrying of the catalyst are formed. With respect to the lattersamples, the surface roughness and initial pressure loss after thealumina coating are measured. The measured results are shown in FIG. 15.As seen from this figure, even when the surface roughness is high orlow, the pressure loss tends to be high.

Similarly, the regeneration experiment after the catching of 6 g/L iscarried out by heating at a discharge temperature of 800° C. The resultsare shown in FIG. 16. As seen from this figure, when the surfaceroughness is large or small, the regeneration ratio is low and theincomplete burning is caused. Moreover, the surface roughness Rz is notmore than 10 μm in case of conducting no surface modification.

As mentioned above, according to Example 2, in the ceramic structuralbody in which the alumina coat layer carrying 60 g/L of the catalyst isformed on the ceramic member, when soot is caught, if the surfaceroughness Rz is not less than 10 μm, the regeneration efficiency in thesoot catching of 10 g/L is high.

Also, when the surface roughness Rz is not less than 100 μm, theregeneration efficiency in the soot catching of 10 g/L becomes low.TABLE 2 Powder A Powder B Powder C Firing silicon carbide metallicsilicon acryl Shaping Dispersing tem- particle particle particle aspectvol assistant medium perature size wt % size wt % size ratio % wt % wt %° C. Sample F1 30 μm 70 1 μm 30 10 μm 1 3 10 18 1600 Sample F2 30 μm 701 μm 30 10 μm 1.5 3 10 18 1600 Sample F3 30 μm 70 1 μm 30 10 μm 2 3 1018 1600 Sample F4 30 μm 70 1 μm 30 10 μm 2.5 3 10 18 1600 Sample F5 30μm 70 1 μm 30 10 μm 3 3 10 18 1600 Sample F6 30 μm 70 1 μm 30 10 μm 3.53 10 18 1600 Sample F7 30 μm 70 1 μm 30 10 μm 4 3 10 18 1600 Sample G130 μm 70 1 μm 30 10 μm 1 3 10 18 1600 Sample G2 30 μm 70 1 μm 30 10 μm1.5 3 10 18 1600 Sample G3 30 μm 70 1 μm 30 10 μm 2 3 10 18 1600 SampleG4 30 μm 70 1 μm 30 10 μm 2.5 3 10 18 1600 Sample G5 30 μm 70 1 μm 30 10μm 3 3 10 18 1600 Sample G6 30 μm 70 1 μm 30 10 μm 3.5 3 10 18 1600Sample G7 30 μm 70 1 μm 30 10 μm 4 3 10 18 1600 Sample H1 30 μm 70 1 μm30 10 μm 1 3 10 18 1600 Sample H2 30 μm 70 1 μm 30 10 μm 1.5 3 10 181600 Sample H3 30 μm 70 1 μm 30 10 μm 2 3 10 18 1600 Sample H4 30 μm 701 μm 30 10 μm 2.5 3 10 18 1600 Sample H5 30 μm 70 1 μm 30 10 μm 3 3 1018 1600 Sample H6 30 μm 70 1 μm 30 10 μm 3.5 3 10 18 1600 Sample H7 30μm 70 1 μm 30 10 μm 4 3 10 18 1600 Sample I1 30 μm 70 1 μm 30 10 μm 1 310 18 1600 Sample I2 30 μm 70 1 μm 30 10 μm 1.5 3 10 18 1600 Sample I330 μm 70 1 μm 30 10 μm 2 3 10 18 1600 Sample I4 30 μm 70 1 μm 30 10 μm2.5 3 10 18 1600 Sample I5 30 μm 70 1 μm 30 10 μm 3 3 10 18 1600 SampleI6 30 μm 70 1 μm 30 10 μm 3.5 3 10 18 1600 Sample I7 30 μm 70 1 μm 30 10μm 4 3 10 18 1600 Sample J1 30 μm 70 1 μm 30 10 μm 1 3 10 18 1600 SampleJ2 30 μm 70 1 μm 30 10 μm 1.5 3 10 18 1600 Sample J3 30 μm 70 1 μm 30 10μm 2 3 10 18 1600 Sample J4 30 μm 70 1 μm 30 10 μm 2.5 3 10 18 1600Sample J5 30 μm 70 1 μm 30 10 μm 3 3 10 18 1600 Sample J6 30 μm 70 1 μm30 10 μm 3.5 3 10 18 1600 Sample J7 30 μm 70 1 μm 30 10 μm 4 3 10 181600 Mold Average Pore Surface Firing roughness Flowing poredistribution rough- time (Ra) amount size ratio ness (Rz) Hr μm m/s μm %μm Sample F1 4 5 5 10 95 8 Sample F2 4 5 5 10 90 8 Sample F3 4 5 5 10 858 Sample F4 4 5 5 10 80 8 Sample F5 4 5 5 10 75 8 Sample F6 4 5 5 10 708 Sample F7 4 5 5 10 65 8 Sample G1 4 10 7 10 95 10 Sample G2 4 10 7 1090 10 Sample G3 4 10 7 10 85 10 Sample G4 4 10 7 10 80 10 Sample G5 4 107 10 75 10 Sample G6 4 10 7 10 70 10 Sample G7 4 10 7 10 65 10 Sample H14 50 9 10 95 50 Sample H2 4 50 9 10 90 50 Sample H3 4 50 9 10 85 50Sample H4 4 50 9 10 80 50 Sample H5 4 50 9 10 75 50 Sample H6 4 50 9 1070 50 Sample H7 4 50 9 10 65 50 Sample I1 4 100 10 10 95 100 Sample I2 4100 10 10 90 100 Sample I3 4 100 10 10 85 100 Sample I4 4 100 10 10 80100 Sample I5 4 100 10 10 75 100 Sample I6 4 100 10 10 70 100 Sample I74 100 10 10 65 100 Sample J1 4 100 15 10 95 110 Sample J2 4 100 15 10 90110 Sample J3 4 100 15 10 85 110 Sample J4 4 100 15 10 80 110 Sample J54 100 15 10 75 110 Sample J6 4 100 15 10 70 110 Sample J7 4 100 15 10 65110

EXAMPLE 3)

In Example 3, sample groups K1-K7, . . . O1-O7 of ceramic memberscomprising of cordierite are prepared by changing pore size, pore sizedistribution and surface roughness, and a platinum-containing aluminacoat layer is formed on the surface of the ceramic member to confirm thefunction and effect thereof. The production conditions of each sampleare shown in Table 3.

The ceramic member in Example 3 is produced through the following steps(1)-(5).

-   (1) As a starting material are mixed 45 wt % of talc (average    particle size: 10 μm), 15 wt % of kaolin (average particle size: 10    μm), 23 wt % of alumina (average particle size: 10 μm), 17 wt % of    silica (average particle size: 10 μm). Thus is called as a    cordierite starting powder.-   (2) In order to prepare a ceramic member having a target pore size    distribution, acryl resin particles having various shapes (density:    1.1 g/cm³) (which is called as powder C) is mixed with the    cordierite starting powder at a given mixing ratio (vol %).-   (3) Then, methyl cellulose as a shaping assistant is mixed at a    given ratio (wt %) to the cordierite starting powder and thereafter    a dispersing medium consisting of an organic solvent and water is    added and all of the starting materials are kneaded.-   (4) The mixture is extrusion-molded with a mold changing a surface    roughness of a mold slit so as to form a target honeycomb form,    whereby a honeycomb shaped body having many through-holes is formed    and either one end portions of these through-holes are plugged in a    checkered pattern to obtain a honeycomb shaped body.-   (5) Finally, the shaped body is dried at 150° C. and degreased at    500° C. and fired in an inert gas atmosphere while passing through    the through-holes at a flow amount shown in Table 3 to obtain sample    groups K1-K7, L1-L7 . . . O1-O7 of honeycomb ceramic member made of    cordierite having a thickness of partition wall of 300 μm, a size of    140 mmφ×150 mm, a cell density of 300 cells/in² a pore size    distribution of 55% and different surface roughnesses.

With respect to each sample, the pore size distribution and surfaceroughness are measured in the same manner as in Example 1 to obtainresults shown in Table 3.

With respect to each sample M1-M7 (maximum roughness Rz=50 μm) belongingto the sample group M having a wall thickness of 300 μm as a typicalexample among the sample groups K, L, . . . O in Example 3, samplesM1′-M7′ and M1″-M7″ are further prepared by changing the wall thicknessto 400 μm and 200 μm, respectively, and initial pressure loss of eachsample having different wall thicknesses is measured by using as afilter while flowing a gas at a section flow rate of 5 m/s. The resultsare shown in FIG. 17. From the results of this figure, as the poredistribution becomes too dense, the initial pressure loss becomes high.Also, even when the pore distribution is rough, the initial pressureloss becomes high. When the wall thickness is 200 μm, the pressure lossis minimum at the pore distribution. of 80-90%, and similarly thepressure loss becomes low at the pore distribution of 75-85% when thewall thickness is 300 μm, and at the pore distribution of 70-80% whenthe wall thickness is 400 μm.

Each of the samples M1-M7, M1′-M7′ and M1″-M7″ is placed as a filter ina path from a diesel engine having a displacement of 3000 cc and anexhaust gas discharged from the engine at a driving state of arevolution umber of 3000 rpm and a torque of 40 Nm is flowed into thefilter for 3 minutes to measure a catching amount of particulates beforeand after the flowing (difference of catching amount in the presence orabsence of the filter), whereby a catching efficiency is measured. Theresults are shown in FIG. 18. As seen from this figure, when the wallthickness is thick, even if the pore distribution is rough, a certainextent of the catching amount is ensured.

Next, samples having pore distribution ratios of 85%, 80% and 75%(K3-K5, L3-L5, M3-M5, N3-N5, O3-O5) are extracted from 7 kinds ofsamples belonging to the sample groups K-O. Among the extracted samples,with respect to the samples having the pore distribution ratio of 85%(K3, L3, M3, N3, O3), there are prepared samples having a wall thicknessof 400 μm (K3′, L3′, M3′, N3′, O3′), and with respect to the sampleshaving the pore distribution ratio of 75% (K5, L5, M5, N5, O5), thereare prepared samples having a wall thickness of 200 μm (K5″, L5″, M5″,N5″, O5″).

With respect to each of these sample groups (K3′, K4, K5″), (L3′, L4,L5″), (M3′, M4, M5″), (N3′, N4, N5″), (O3′, O4, O5″), the pressure lossin the catching of particulates (soot) is measured. The data after thecatching of 6 g/L are shown in FIG. 19. Also, a regeneration experimentis carried out by heating at a discharge temperature of 800° C. toobtain results shown in FIG. 20. As shown in these figures, as thesurface roughness Rz is too small or too large, the pressure loss ishigh and the regeneration ratio lowers. As each of these samples is cutand observed, when the surface roughness is small, the aggregation ofthe particulates is observed, while even if the surface roughness is toolarge, the particulates are retained. This is considered due to thedegree of disorder flow of the exhaust gas.

Then, each sample of the above sample groups (K3′, K4, K5″), (L3′, L4,L5″), (M3′, M4, M5″), (N3′, N4, N5″), (O3′, O4, O5″) is impregnated in a0.1% solution of hydrogen fluoride (hydrogen acid) for 1 minute andthereafter an alumina coat layer of 60 g/L is formed and 2 g/L of aplatinum (Pt) catalyst is carried on the alumina coat layer, wherebysamples having different surface roughnesses of alumina coat layer afterthe carrying of the catalyst are formed. With respect to the lattersamples, the surface roughness and initial pressure loss after thealumina coating are measured. The measured results are shown in FIG. 21.As seen from this figure, even when the surface roughness is high orlow, the pressure loss tends to be high.

Further, the regeneration experiment after the catching of 6 g/L iscarried out with respect to each sample after the formation of thecatalyst coat layer. The results are shown in FIG. 22. As seen from thisfigure, when the surface roughness is large or small, the regenerationratio is low and the incomplete burning is caused. Moreover, the surfaceroughness Rz is not more than 10 μm in case of conducting no surfacemodification.

As mentioned above, according to Example 3, in the ceramic structuralbody in which the alumina coat layer carrying 60 g/L of the catalyst isformed on the ceramic member, when soot is caught, if the surfaceroughness Rz is not less than 10 μm, the regeneration efficiency in thesoot catching of 10 g/L is high.

Also, when the surface roughness Rz is not less than 100 μm, theregeneration efficiency in the soot catching of 10 g/L becomes low.TABLE 3 Powder C Firing Mold Average Pore Surface acryl ShapingDispersing tem- Firing roughness Flowing pore distribution rough-particle aspect vol assistant medium perature time (Ra) amount sizeratio ness (Rz) size ratio % wt % wt % ° C. Hr μm m/s μm % μm Sample K110 μm 1 3 10 18 800 6 5 5 10 95 8 Sample K2 10 μm 1.5 3 10 18 800 6 5 510 90 8 Sample K3 10 μm 2 3 10 18 800 6 5 5 10 85 8 Sample K4 10 μm 2.53 10 18 800 6 5 5 10 80 8 Sample K5 10 μm 3 3 10 18 800 6 5 5 10 75 8Sample K6 10 μm 3.5 3 10 18 800 6 5 5 10 70 8 Sample K7 10 μm 4 3 10 18800 6 5 5 10 65 8 Sample L1 10 μm 1 3 10 18 800 6 10 7 10 95 10 SampleL2 10 μm 1.5 3 10 18 800 6 10 7 10 90 10 Sample L3 10 μm 2 3 10 18 800 610 7 10 85 10 Sample L4 10 μm 2.5 3 10 18 800 6 10 7 10 80 10 Sample L510 μm 3 3 10 18 800 6 10 7 10 75 10 Sample L6 10 μm 3.5 3 10 18 800 6 107 10 70 10 Sample L7 10 μm 4 3 10 18 800 6 10 7 10 65 10 Sample M1 10 μm1 3 10 18 800 6 50 9 10 95 50 Sample M2 10 μm 1.5 3 10 18 800 6 50 9 1090 50 Sample M3 10 μm 2 3 10 18 800 6 50 9 10 85 50 Sample M4 10 μm 2.53 10 18 800 6 50 9 10 80 50 Sample M5 10 μm 3 3 10 18 800 6 50 9 10 7550 Sample M6 10 μm 3.5 3 10 18 800 6 50 9 10 70 50 Sample M7 10 μm 4 310 18 800 6 50 9 10 65 50 Sample N1 10 μm 1 3 10 18 800 6 100 10 10 95100 Sample N2 10 μm 1.5 3 10 18 800 6 100 10 10 90 100 Sample N3 10 μm 23 10 18 800 6 100 10 10 85 100 Sample N4 10 μm 2.5 3 10 18 800 6 100 1010 80 100 Sample N5 10 μm 3 3 10 18 800 6 100 10 10 75 100 Sample N6 10μm 3.5 3 10 18 800 6 100 10 10 70 100 Sample N7 10 μm 4 3 10 18 800 6100 10 10 65 100 Sample O1 10 μm 1 3 10 18 800 6 100 15 10 95 110 SampleO2 10 μm 1.5 3 10 18 800 6 100 15 10 90 110 Sample O3 10 μm 2 3 10 18800 6 100 15 10 85 110 Sample O4 10 μm 2.5 3 10 18 800 6 100 15 10 80110 Sample O5 10 μm 3 3 10 18 800 6 100 15 10 75 110 Sample O6 10 μm 3.53 10 18 800 6 100 15 10 70 110 Sample O7 10 μm 4 3 10 18 800 6 100 15 1065 110

INDUSTRIAL APPLICABILITY

The ceramic honeycomb structural body according to the invention is usedin an exhaust gas purification apparatus in an engine using a fossilfuel such as diesel engine or the like, or a boiler.

1. A honeycomb structural body comprising one or plural pillar-shapedporous ceramic members in which many through-holes are arranged side byside in a longitudinal direction through partition walls and either oneend portions of these through-holes are plugged, characterized in thatthe partition wall forming the structural body has a surface roughnessof not less than 10 μm as a maximum roughness Rz defined in JISB0601-2001 and an average pore size of 5-100 μm in a pore distributionmeasured by a mercury pressure method, and satisfies the followingrelationship:A≦90−B/20 when a ratio pores having a pore size of 0.9-1.1 times theaverage pore size to total pore volume is A (%) and a thickness of thepartition wall is B (μm).
 2. A honeycomb structural body comprising oneor plural pillar-shaped porous ceramic members in which manythrough-holes are arranged side by side in a longitudinal directionthrough partition walls and either one end portions of thesethrough-holes are plugged, characterized in that the partition wallforming the structural body has a surface roughness of not less than 10μm as a maximum roughness Rz defined in JIS B0601-2001 and an averagepore size of 5-100 μm in a pore distribution measured by a mercurypressure method, and satisfies the following relationship:A≦100−B/20 when a ratio pores having a pore size of 0.9-1.1 times theaverage pore size to total pore volume is A (%) and a thickness of thepartition wall is B (μm).
 3. A honeycomb structural body according toclaim 1, wherein the partition wall forming the structural body has asurface roughness of not less than 10 μm as a maximum roughness Rzdefined in JIS B0601-2001 and an average pore size of 5-100 μm in a poredistribution measured by a mercury pressure method, and satisfies thefollowing relationship:A≦100−B/20 when a ratio pores having a pore size of 0.9-1.1 times theaverage pore size to total pore volume is A (%) and a thickness of thepartition wall is B (μm).
 4. A honeycomb structural body according toclaim 1, wherein a maximum roughness Rz showing the surface roughness isnot more than 100 μm.
 5. A honeycomb structural body according to claim1, wherein the surface of the partition wall separating the through-holeis provided with a coating layer of a catalyst.
 6. A honeycombstructural body according to claim 1, wherein the porous ceramic membersare bundled by interposing a sealing material layer between saidmembers.
 7. A honeycomb structural body according to claim 1, whereinthe porous ceramic member is made of a silicon carbide ceramic.
 8. Ahoneycomb structural body according to claim 1, wherein said body isused as a filter for an exhaust gas purification apparatus in a vehicle.